In present medical technology, delivering the drug to a lesion zone without passing the metabolism of the digestive system and the liver to maintain the concentration of the drug in the blood is a concerned research subject. However, it is difficult to deliver the drug to the lesion zone directly.
For example, the direct delivery of drugs to the central nervous system would make the resulting interactions highly target-specific and thereby dramatically improve the therapeutic effects and reduce possible side effect. However, it is difficult to delivery many potent therapeutic agents to the brain due to the presence of the blood-brain barrier (BBB), which is a specialized system of capillary endothelial cells that protects the brain from harmful substances. Although many methods have been developed to overcome BBB impermeability when delivering drugs, such as increasing their liquid solubility, or by the using vectors such as amino acids for carriers, none has been applied clinically.
Recently, focus ultrasound (FUS) can be used to transiently disrupt the BBB and thereby aid the noninvasive delivery of treatment agents to specific regions in the brain. Furthermore, gas-filled microbubbles (MBs) were originally developed as an intravascular contrast agent to enhance backscattering signals in ultrasound imaging. Therefore, the technique of transmitting FUS with usage of MBs is well-known as a strategy of increasing BBB permeability and therefore is able to improve the efficiency of drug delivery. The mechanical force caused by MBs inertial cavitation provides a non-invasive, transient, and reversible BBB disruption. However, although using the abovementioned method can improve the efficiency of the drug delivery, how to estimate treating conditions of an affected part of a patient is another issue for clinical staffs.
In the current technology for processing focused ultrasound therapy, several imaging modalities including magnetic resonance imaging (MRI), positron emission tomography (PET), and single photon emission computed tomography (SPECT) and contrast-enhanced ultrasound (CEUS) have been used to monitor drug pharmacokinetics. For example, MRI can also provide helpful imaging guidance not only to localize the targeting region, but also to observe the course of FUS transmission. However, it is necessary to take MRI before and after surgery, respectively, so that the clinical staff needs to go forward and backward between an operation room and an imaging room. Therefore, it is difficult to obtain real-time images for monitoring the operation status of the surgery easily. Except for the abovementioned disadvantage, it is also a load to vigor of the patient.